Suicide is a leading cause of death in children and adolescents and a critical public health concern. One promising suicide prevention strategy that is under-utilized includes reducing access to lethal means, or means restriction. Firearms are an important target for means restriction given that 1 in 3 homes possess a firearm and firearms are the most lethal manner by which suicide is attempted. Primary care is an ideal setting in which to provide firearms means restriction given that almost half of youth who die by suicide do not access specialty mental health services in the 12 months preceding their attempt. The Safety Check intervention is an evidence-based practice for implementing firearms means restriction in pediatric primary care (including pediatrics, family medicine, and adolescent medicine). Despite the existence of this intervention and recommendations from the American Academy of Pediatrics, providers rarely discuss means restriction or firearms during visits, suggesting the need for a better understanding of the barriers and facilitators to implementing means restriction in pediatric primary care. Implementation science frameworks, including the Consolidated Framework for Implementation Research (CFIR), suggest the importance of attending to multiple levels of context during implementation, including provider (e.g., self-efficacy), organizational (e.g., expectations about provider behavior), system (e.g., prompts in the electronic health records), and intervention (e.g., acceptability) factors. The NIMH-funded Mental Health Research Network (MHRN), a consortium of 13 healthcare systems across the United States, affords a unique opportunity to better understand how to implement means restriction in pediatric primary care from a system-level perspective. Our objective in this application is to collaboratively develop implementation strategies in partnership with MHRN stakeholders to increase the use of means restriction in pediatric primary care. In Aim 1, we will survey leadership of 96 primary care practices within 2 MHRN systems (Henry Ford Health System and Baylor, Scott, & White Health) to understand acceptability and use of the three components of the Safety Check intervention (i.e., screening, brief counseling around gun safety, and provision of gunlocks). In Aim 2, in collaboration with MHRN stakeholders in these 2 systems, we will use intervention mapping and the CFIR for to systematically develop and evaluate a multi-level menu of implementation strategies for firearm means restriction in pediatric primary care. The proposed work is consistent with the NIMH strategic plan, specifically Objective 4, to strengthen the public health impact of NIMH-supported research, and will lead to a hybrid effectiveness-implementation R01 proposal. The long-term goal of this line of research is to reduce death by suicide by increasing the use of evidence-based strategies in pediatric primary care while also promoting multi-level implementation strategies informed by a systematic and rigorous development approach.